doc.: ieee 802.15-01/026r1 submission march 2001 jie liang, texas instrumentsslide 1 jie liang texas...
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March 2001
Jie Liang, Texas InstrumentsSlide 1
doc.: IEEE 802.15-01/026r1
Submission
Jie Liang
Texas Instruments Incorporated
12500 TI Blvd.
Dallas, Texas 75243
(ph) 214-480-4105
(email) [email protected]
Proposal for Non-Collaborative BT and 802.11b MAC Mechanisms for
Enhanced Coexistence
March 2001
Jie Liang, Texas InstrumentsSlide 2
doc.: IEEE 802.15-01/026r1
Submission
Outline
• Summary of our ACL proposal
• Focus on updated proposal to improve the BT voice link quality while improving 802.11b throughput
• Proposals for improving BT voice links:– Selecting HV3 packet as default packet type for SCO link
– Enhanced voice link: allow Master flexibility to search for best TX slots given delay requirement
• Simulation results that confirm significant improvement in throughput for both BT and 802.11b
March 2001
Jie Liang, Texas InstrumentsSlide 3
doc.: IEEE 802.15-01/026r1
Submission
Summary of ACL Proposals
• Adaptive packet type selection considering slot time,
FEC, CRC based on channel condition and QoS:
DM1, DM3, DM5, DH1, DH3, DH5,AUX1
• Adaptive packet payload length selection: fragmentation
• Adaptive link configuration: flow control, rate control
March 2001
Jie Liang, Texas InstrumentsSlide 4
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Submission
SCO Link Coexistence Problems
March 2001
Jie Liang, Texas InstrumentsSlide 5
doc.: IEEE 802.15-01/026r1
Submission
SCO Link Coexistence Problem and Scenarios
• A serious problem that needs urgent solutions• Voice applications are among the most important
applications for BT• Significant packet losses for BT SCO links under
802.11b interference• Significant throughput drop for 802.11b network
• Scenarios• Separated > 10 feet: minor problem• Problem when <10 feet distance• Also dependent on 802.11b duty cycle
March 2001
Jie Liang, Texas InstrumentsSlide 6
doc.: IEEE 802.15-01/026r1
Submission
Key Ideas
• HV3 packet type is the most coexistence friendly compared with HV1 and HV2 packets
• Allow the master to search for the best TX slots given a delay requirement
March 2001
Jie Liang, Texas InstrumentsSlide 7
doc.: IEEE 802.15-01/026r1
Submission
Voice Payload and SCO Packets
• QoS requirement of voice payload:– PCM coding: 10-4 (random errors) good quality is retained
10-3 start to notice artifacts, but still acceptable– CVSD coding: 10-3 good quality is retained
10-2 start to notice artifacts, but still acceptable– Perceptible errors mostly come from collisions (really high BER or fail to
decode the BT packet header)
• HV1 vs. HV2 vs. HV3– Packet payload length: 80, 160, 240 bits (1.25ms, 2.5ms, 3.75ms)– Tsco = 2, 4, 6– FEC 1/3, 2/3, none
March 2001
Jie Liang, Texas InstrumentsSlide 8
doc.: IEEE 802.15-01/026r1
Submission
802.11b Channel Access Timing
Busy Medium
DIFS
Back-off Window
Medium Idle
New Frame
ACK
Frame Exchange Sequences
Tcp
SIFS
Tbf
SIF= 10us DIF = 50us aSlot_time = 20usTbf = N x aSlotTf=PLCP Preamble + Header = 192us
Minimum Time Needed (no back-off and payload):Tm= DIFS+Tf+SIFS+Tf=50+192+10+192=444us
500bytes Payload (add back-off and Payload at 11Mbps): T=16xaSlot+Tm+400=1164us
Note: needs about 2 BT Slot time for transmitting one average packet for 11Mbps 802.11b (a block of time is needed by 802.11b)
March 2001
Jie Liang, Texas InstrumentsSlide 9
doc.: IEEE 802.15-01/026r1
Submission
Adaptive SCO Link Configuration
Proposal: Use HV3 packet as default (more co-existence friendly)
• Leave more time for 802.11 transmissions• Lack of FEC in HV3 is not problem
high tolerance of random BER FEC does not help during collision
• Transmit less often – good for saving power
HV1 Traffic
HV3 Traffic
March 2001
Jie Liang, Texas InstrumentsSlide 10
doc.: IEEE 802.15-01/026r1
Submission
Enhanced Voice Link (1)
• New SCO packet type – EV3:– no FEC
– 240 bits payload
– One EV3 packet for every 6 slots (delay<3.75ms)
– Slave will only transmit when addressed by master• Only master needs to do the scheduling• Make sure only one pair of slots are used
– CRC: could be another option, which accommodate applications that want data integrity on voice data
• Why:– Flexible in traffic scheduling to avoid collisions (no fixed intervals)
March 2001
Jie Liang, Texas InstrumentsSlide 11
doc.: IEEE 802.15-01/026r1
Submission
Enhanced Voice Link (2)
• Enhanced Voice Link Setup:
new EV3 packet type, payload size: 240 bits
Npoll: <6 slots
• Adaptive selection of transmitting slots based on channel conditions
• Delay < 3.75ms
EV3 Traffic
HV3 Traffic
B B G GG G B G
B B G GG G B G
March 2001
Jie Liang, Texas InstrumentsSlide 12
doc.: IEEE 802.15-01/026r1
Submission
Algorithm for Selecting TX Slots
Score(n) = 0, if hop(2*n) and hop(2*n+1) are both bad channels 1, if hop(2*n) is bad and hop(2*n+1) is good 2, if hop(2*n) is good and hop(2*n+1) is bad 3, if both are good channels
TxSlot=0; MaxScore=0;For(n=0;n<3;n++)
if(Score(n)>MaxScore) TxSlot=2*n; MaxScore = Score(n);
B B G G B G
0 1 2 3 4 5hop
score 0 3 1
Selecting a pair of slots
with the maxim score
March 2001
Jie Liang, Texas InstrumentsSlide 13
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Submission
Simulation Results
• OPNET models for 802.11b and BT baseband
• Only considered collisions in radio link:– In-band packets that overlap in time result in collision– Collision meant packet loss– Valid assumption for the considered scenario (<3 feet
separation) and voice payload’s tolerance for random errors
• Two 802.11b stations and two BT stations in simulations
March 2001
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Submission
OPNET Scenario
March 2001
Jie Liang, Texas InstrumentsSlide 15
doc.: IEEE 802.15-01/026r1
Submission
Simulation Results – Key Points
• Note changes from first 15 sec (BT silence) to the second 15 sec
• Note that the enhanced voice link always outperforms HV3 and HV1 links for both BT throughput and 802.11b throughput
• Note that HV3 is better than HV1 for coexistence• Note that the changes in behavior when loads on
802.11b networks change (from 5Mbps ->2Mbps
->200k)
March 2001
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doc.: IEEE 802.15-01/026r1
Submission
HV1 Packet
WLAN Load: 5 Mbps
March 2001
Jie Liang, Texas InstrumentsSlide 17
doc.: IEEE 802.15-01/026r1
Submission
HV3 Packets
WLAN Load: 5 Mbps
March 2001
Jie Liang, Texas InstrumentsSlide 18
doc.: IEEE 802.15-01/026r1
Submission
Enhanced Voice Link
WLAN Load: 5 Mbps
March 2001
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Submission
BT Master-Slave Throughput
WLAN Load: 5 Mbps
March 2001
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Submission
802.11b Throughput
WLAN Load: 5 Mbps
March 2001
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Submission
BT Master-Slave Throughput
WLAN Load: 2 Mbps
March 2001
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Submission
802.11b Throughput
WLAN Load: 2 Mbps
March 2001
Jie Liang, Texas InstrumentsSlide 23
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Submission
BT Master-Slave Throughput
WLAN Load: 200kbps
March 2001
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doc.: IEEE 802.15-01/026r1
Submission
802.11b Throughput
WLAN Load: 200kbps
March 2001
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doc.: IEEE 802.15-01/026r1
Submission
Conclusions (1)
• Proposals for enhancing voice links for BT:– HV3 packet as default SCO packet type– Enhanced voice link using new EV3 packet
• Extensive simulation data demonstrates that the proposed methods significantly improve coexistence performance
• No changes to the current BT specs, just new usages
• Easy implementation through software upgrades
March 2001
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Submission
Conclusions (2)Evaluation Questionnaires
• Non-Collaborative• Impact on Standards:
– New SCO packet type
• Regulatory Impact:– None
• Complexity:– Software upgrade for most implementations
• Interoperability with Non-coexistence Devices:– Drop back to HV3 packet for non-coexistence devices
March 2001
Jie Liang, Texas InstrumentsSlide 27
doc.: IEEE 802.15-01/026r1
Submission
Conclusions (3) Evaluation Questionnaires
• Classes of Operations:– Both PCF and DCF for 802.11b– Voice payload for BT
• Voice and Data Support:– Voice
• Impact on higher layer:– Mostly none
• Impact on Power Management:– None